Maruti Suzuki — bad mileage

Address:

Delhi

i have maruti new swift diesel VDI. Its performance has been degrading since purchase. its showing an average of 11 km /liter on meter as wel as recorded from performance. i have shown it in service center but they say its details from the check m eter regarding pressure and all data is correct, so why its giving such low average. It has undergone a distance of 6000 km. so please suggest me where to get this problem rectified..my email id is [protected]@yahoo.co.in.. thax..